1. Field of the Invention
The present invention relates to a new and improved procedure for the preparation of monochloro-diamino-s-triazines of known herbicidal activity. The monochloro-diamino-s-triazines are obtained by the present procedure not only in high yield and excellent product quality, but also without giving rise to problems in effluent treatment and disposal.
2. Description of the Prior Art
The herbicidal activity of various monochloro-diamino-s-triazines has been described, for example, in Gysin et al. U.S. Pat. No. 2,891,855. One such monochloro-diamino-s-triazine, which is commercially useful as a herbicide, is 2-chloro-4-ethylamino-6-isopropylamino-s-triazine. This compound is commercially available as an atrazine herbicide. The aforesaid 2-chloro-4-ethylamino-6-isopropylamino-s-triazine can, as described in the Gysin et al. patent referred to above, be prepared from cyanuric chloride and the corresponding organic amines.
The synthesis ordinarily proceeds via the formation of the 2,4-dichloro-6-isopropylamino-s-triazine intermediate compound in accordance with the following reaction: ##STR1## The 2,4-dichloro-6-isopropylamino-s-triazine compound is thereafter converted to the active compound, i.e., 2-chloro-4-ethylamino-6-isopropylamino-s-triazine, referred to as atrazine, by reaction with monoethylamine, as follows: ##STR2##
The first step (equation A above) is accompanied by a number of undesirable side reactions, which may for example involve the hydrolysis of some of the chloro-amino-s-triazines or the formation of various by-products, such as, 2-chloro-4,6-bis-isopropylamino-s-triazine. The undesired formation of the last mentioned material, where the preparation of the atrazine product is concerned, may proceed in accordance with the following reaction scheme: ##STR3##
In the preparation of 2-chloro-4,6-diamino-s-triazines and, by way of illustration, of the atrazine herbicide, i.e., 2-chloro-4-ethylamino-6-isopropylamino-s-triazine, it will be appreciated that it is desirable to minimize the co-production of the by-product illustrated in equation (C) and of other by-products, thereby avoiding difficulties in isolating the desired atrazine product when said product is produced on a large scale. It is also highly desirable to produce the 2-chloro-4,6-diamino-s-triazines in high yield and purity without creating problems in effluent treatment and disposal because of the aqueous NaCl and triazine by-products contained in the aqueous effluent of the above described process of manufacture.
U.S. Pat. No. 3,328,399 discloses a process for preparing amino-s-triazines without neutralizing the HCl formed in the reaction. However, this patent discloses only a method involving reacting cyanuric chloride with secondary amines in an anhydrous system and the HCl formed is distilled off from the reaction mixture.
This method of amino-s-triazine preparation cannot be extended to monoalkylamines. Unhindered monoalkylamine hydrochlorides can react under the conditions described to form bistriazines, a reaction not possible with secondary amines; ##STR4##
In addition, as the reactivities of the second and third chlorine on the cyanuric chloride molecule are not substantially different, monoalkylamines do not exhibit sufficient selectivity to stop after substitution of two chlorines; rather a mixture of mono-, di-, and tri-substituted triazines is formed in contrast to the selectivity of the less reactive secondary amines: ##STR5##
Unhindered monoalkylamines may form bis-triazines in the second stage also as shown: ##STR6##
The lack of selectivity of monoalkylamines in the second step of the reaction and the tendency to form bis-triazines in both stages precludes atrazine-type herbicides by the conditions of U.S. Pat. No. 3,328,399.
And U.S. Pat. No. 3,586,679 discloses a process for the production of only dichloro-monoamino-s-triazines in an anhydrous medium with no provision for conversion to monochloro-diamino-s-triazines in a caustic-free manner.